Mirror device, mirror drive method, light irradiation device, and image acquisition device

ABSTRACT

Provided is a mirror device including a mirror which is supported to be flappable around a fast axis and supported to be flappable around a slow axis and in which a resonance frequency of flapping thereof with respect to the fast axis is a first value and a resonance frequency of the flapping thereof with respect to the slow axis is a second value lower than the first value; a signal extracting portion configured to obtain from a slow axis coil a synthesized signal including an induced signal generated in the slow axis coil due to an operation of flapping the mirror around the fast axis and configured to extract the induced signal from the synthesized signal; and a signal generating portion configured to generates a driving signal so that the flapping of the mirror with respect to the fast axis is in a resonance state according to the induced signal.

TECHNICAL FIELD

The present disclosure relates to a mirror device, a mirror drivemethod, a light irradiation device, and an image acquisition device.

BACKGROUND ART

Patent Document 1 discloses an electromagnetically driven scanningmirror. The scanning mirror is controlled such that it flaps around apredetermined axis in a resonance state. A control signal for drivingthe scanning mirror is generated using a counter-electromotive forcegenerated by driving the scanning mirror.

CITATION LIST Patent Documents

[Patent Document 1] Japanese Unexamined Patent Publication No.2009-258321

SUMMARY OF INVENTION Technical Problem

In the device of Patent Document 1, since the counter electromotiveforce is detected in a form in which it has been added to the drivingsignal, it is necessary to extract a signal component corresponding tothe counter electromotive force from the detected signal. However, afrequency of the driving signal and a frequency of the counterelectromotive force are the same, and an amplitude of the counterelectromotive force with respect to an amplitude of the driving signalis small. Therefore, it is difficult to extract a component of thecounter electromotive force from the detected signal. Since the drivingsignal of the scanning mirror is generated using the counterelectromotive force, it is difficult to reliably drive the scanningmirror in the resonance state when it is difficult to extract thecomponent of the counter electromotive force.

Therefore, an object of the present disclosure is to provide a mirrordevice capable of driving a mirror in a resonance state, a mirror drivemethod, a light irradiation device, and an image acquisition device.

Solution to Problem

One embodiment of the present disclosure is a mirror device. The mirrordevice includes a mirror supported to be flappable around a first driveaxis and supported to be flappable around a second drive axisintersecting the first drive axis and in which a resonance frequency offlapping thereof with respect to the first drive axis is a first valueand a resonance frequency of the flapping thereof with respect to thesecond drive axis is a second value lower than the first value; a firstdrive portion configured to flap the mirror around the first drive axis;a second drive portion configured to flap the mirror around the seconddrive axis; a signal extracting portion configured to obtain from thesecond drive portion a synthesized signal including an induced signalgenerated in the second drive portion due to an operation of flappingthe mirror around the first drive axis and configured to extract theinduced signal from the synthesized signal; and a signal generatingportion configured to generate a driving signal which controls the firstdrive portion so that the flapping of the mirror with respect to thefirst drive axis is in a resonance state according to the extractedinduced signal.

Another embodiment of the present disclosure is a mirror drive method.The driving method is for a mirror which is supported to be flappablearound a first drive axis and is supported to be flappable around asecond drive axis intersecting the first drive axis and in which aresonance frequency of flapping thereof with respect to the first driveaxis is a first value and a resonance frequency of the flapping thereofwith respect to the second drive axis is a second value lower than thefirst value, the method including a step (flapping step) of controllinga first drive portion such that the mirror flaps around the first driveaxis; a step (acquiring step) of obtaining from a second drive portion asynthesized signal including an induced signal generated in the seconddrive portion due to an operation of flapping the mirror around thefirst drive axis; a step (extracting step) of extracting the inducedsignal from the synthesized signal; and a step (generating step) ofgenerating a driving signal which controls the first drive portion sothat the flapping of the mirror with respect to the first drive axis isin a resonance state according to the extracted induced signal.

The mirror is flapped around the first drive axis by the first driveportion. While this mirror is flapping around the first drive axis, thesignal extracting portion obtains the synthesized signal from the seconddrive portion. This synthesized signal includes the induced signalgenerated in the second drive portion due to the operation of flappingthe mirror around the first drive axis. Since the induced signal iscaused by the operation of the first drive portion, a frequency thereofcorresponds to a frequency of the flapping of the mirror with respect tothe first drive axis. Since the frequency of the flapping of the mirrorwith respect to the first drive axis is higher than the frequency of themirror with respect to the second drive axis, it is possible to easilyextract the induced signal from the signal obtained from the seconddrive portion. Additionally, the signal generating portion generates adriving signal which is provided to the first drive portion according tothe induced signal. Therefore, it is possible to obtain a result offlapping the mirror with the first drive portion according to theinduced signal from the second drive portion. Accordingly, since afeedback loop system relating to the flapping of the mirror with respectto the first drive axis is formed, it is possible to reliably drive themirror with respect to the first drive axis in a resonance state.

The signal generating portion may generate the driving signal accordingto a phase difference between a phase of the driving signal input fromthe signal generating portion to the first drive portion and a phase ofthe induced signal obtained by the signal extracting portion. Further,the generating step may generate the driving signal according to a phasedifference between a phase of the driving signal input to the firstdrive portion and a phase of the induced signal obtained in theextracting step. Furthermore, the signal generating portion may generatethe driving signal so that the phase difference becomes a constantvalue. Also, the generating step may generate the driving signal so thatthe phase difference becomes a constant value. Further, the signalgenerating portion may generate the driving signal to reduce the phasedifference. The generating step may generate the driving signal so thatthe phase difference becomes small. According to these configurations, adifference between a frequency of the driving signal and a resonancefrequency in the locking of the mirror with respect to the first driveaxis is indicated as a phase difference between the phase of the drivingsignal and the phase of the induced signal. The frequency of the drivingsignal can be easily adjusted to the resonance frequency by adjustingthe frequency of the driving signal so that this phase difference is setto be a constant value or to be small. The constant value may be zero.

The signal generating portion may generate the driving signal accordingto an amplitude of the induced signal obtained by the signal extractingportion. The generating step may generate the driving signal accordingto an amplitude of the induced signal obtained in the extracting step.Further, the signal generating portion may generate the driving signalso that the amplitude of the induced signal increases. Further, thegenerating step may generate the driving signal so that the amplitude ofthe induced signal increases. According to these configurations, thedifference between the frequency of the driving signal and the resonancefrequency in the flapping of the mirror with respect to the first driveaxis is indicated as the amplitude of the induced signal. The frequencyof the driving signal can be easily adjusted to the resonance frequencyby adjusting the frequency of the driving signal so that the amplitudebecomes large.

The signal extracting portion may include a signal filter portion, andthe signal filter portion may pass a signal including a frequency higherthan the second value. Further, in the extracting step, a signalincluding a frequency higher than the second value may be passed by thesignal filter portion. Further, the signal filter portion may attenuatea signal including a frequency smaller than the second value.Furthermore, in the extracting step, the signal filter portion mayattenuate a signal including a frequency smaller than the second value.According to these configurations, the induced signal can be accuratelyextracted from the synthesized signal.

The signal extracting portion may include a signal amplifier, and thesignal amplification portion may amplify a signal including a frequencyhigher than the second value. In the extracting step, the signalamplifier may amplify a signal including a frequency higher than thesecond value. According to these configurations, the induced signal canbe accurately extracted from the synthesized signal.

Yet another embodiment of the present disclosure is a light irradiationdevice which irradiates light on an object. The light irradiation deviceincludes a light source configured to output light, and a mirror deviceconfigured to scan the light output from the light source. Still anotherembodiment of the present disclosure is a light irradiation method whichirradiates light onto an object. The light irradiation method includesan output step of outputting light from a light source, and theabove-described mirror drive method which scans the light output fromthe light source. Yet still another embodiment of the present disclosureis an image acquisition device which obtains an image of an object. Theimage acquisition device includes the above-described light irradiationdevice, and a photodetector configured to detect light generated in theobject according to radiation of the light by the light irradiationdevice. Further, yet still another embodiment is an image acquiringmethod for acquiring an image of an object. The image acquiring methodincludes the above-described light irradiating method and a detectionstep of detecting light generated in the object in accordance with thelight irradiation by the light irradiating method. According to theseaspects, since the mirror device can reliably drive the mirror in theresonance state around the first drive axis, the light irradiation andthe image acquisition can be reliably performed.

Advantageous Effects of Invention

According to the embodiment, a mirror device capable of driving a mirrorin a resonance state, a mirror drive method, a light irradiation device,and an image acquisition device are provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a configuration of a mirror deviceaccording to an embodiment.

FIG. 2 is an exploded perspective view of a mirror unit shown in FIG. 1.

FIG. 3 is a perspective view showing a mirror structure shown in FIG. 2.

FIG. 4 is a perspective view showing an arrangement of a first coil anda second coil in the mirror structure.

FIG. 5 is a block diagram showing a configuration of the control unitshown in FIG. 1.

FIGS. 6A-6F are diagrams showing signals handled in a control unit.

FIG. 7 is a diagram showing a band of a signal extracted in a signalextraction unit shown in FIG. 5.

FIG. 8 is a block diagram showing a configuration of a controller shownin FIG. 5.

FIG. 9 is a graph showing a phase relationship between a driving signaland an induced signal and an amplitude relationship between the drivingsignal and the induced signal.

FIG. 10 is a diagram showing main steps in a mirror drive method.

FIG. 11 is a block diagram showing a configuration of a controllerincluded in a control unit according to a modified example.

FIG. 12 is a block diagram showing a configuration of a controllerincluded in a control unit according to another modified example.

FIG. 13 is a block diagram showing a configuration of a control unitaccording to yet another modified example.

FIG. 14 is a schematic diagram showing a configuration of a lightirradiation device including a mirror device.

FIG. 15 is a schematic diagram showing a configuration of an imageacquisition device including a mirror device.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a mirror device, a mirror drive method, a light irradiationdevice, and an image acquisition device will be described in detail withreference to the accompanying drawings. In the description of thedrawings, the same elements are designated by the same referencenumerals, and duplicate descriptions will be omitted.

As shown in FIG. 1, a mirror device 1 according to the embodimentincludes a mirror unit 2 and a control unit 3. Light L1 is incident onthe mirror unit 2. The light L1 includes, for example, coherent lightsuch as laser light, or incoherent light such as light output from alight emitting diode. Additionally, the mirror unit 2 reflects theincident light L1 while changing an optical path of reflected light L2.The control unit 3 inputs a driving signal to the mirror unit 2. Theoptical path of the reflected light L2 is controlled on the basis ofthis driving signal.

FIG. 2 is an exploded perspective view of the mirror unit 2. Forconvenience of explanation, X, Y and Z axes are provided in each of thedrawings. As shown in FIG. 2, the mirror unit 2 has a mirror structure10, a lower magnetic body 20, a cap structure 30, and a casing 40. Thecasing 40 has a substantially rectangular parallelepiped shape andaccommodates the mirror structure 10 and the lower magnetic body 20. Thelower magnetic body 20 is disposed on a bottom surface 42 of the casing40. The mirror structure 10 is disposed above the lower magnetic body 20(a positive side of the Z axis). The cap structure 30 is disposed tocover an opening portion 41 of the casing 40.

A configuration of the mirror structure 10 will be described in detailwith reference to FIGS. 3 and 4. FIG. 3 is a perspective view of themirror structure 10. FIG. 4 is a perspective view showing an arrangementof a second coil 17 a and a first coil 18 a in the mirror structure 10.As shown in FIGS. 3 and 4, the mirror structure 10 includes a supportportion 11, a second movable portion 12, a first movable portion 13, anda mirror 16. The second movable portion 12 is connected to the supportportion 11. The first movable portion 13 is connected to the secondmovable portion 12. The mirror 16 is supported by the first movableportion 13.

The support portion 11 is a frame body and has a rectangular shape whenseen in the Z axis direction. A rectangular opening portion 11 a isprovided in the support portion 11. A pair of substantially rectangularconcave portions 11 b and 11 b are provided on two sides of an outeredge of the opening portion 11 a which extend in the X axis direction.

The second movable portion 12 is disposed in the opening portion 11 a ofthe support portion 11. The second movable portion 12 is connected tothe support portion 11 by a pair of second beam portions 14 and 14.Further, the second movable portion 12 is physically connected to thefirst movable portion 13 by a pair of first beam portions 15 and 15. Thepair of second beam portions 14 and 14 are located on a straight line A2parallel to the Y axis and are provided on both sides of the secondmovable portion 12. The second beam portion 14 supports the secondmovable portion 12 to be flappable around the straight line A2 withrespect to the support portion 11. The second beam portion 14 has ameandering shape when seen in the Z direction. According to such ashape, the second beam portion 14 has a relatively small torsionalrigidity around the straight line A2. The second movable portion 12 hasa rectangular opening portion 12 a.

The first movable portion 13 is a frame body and has a rectangular shapewhen seen in the Z axis direction. A rectangular opening portion 13 a isprovided in the first movable portion 13. The first movable portion 13is connected to the second movable portion 12 by the pair of first beamportions 15 and 15. Further, the first movable portion 13 is physicallyconnected to the mirror 16. The pair of first beam portions 15 and 15are located on a straight line A1 parallel to the X axis and areprovided on both sides of the first movable portion 13. The first beamportion 15 supports the first movable portion 13 to be flappable aroundthe straight line A1 with respect to the second movable portion 12. Thefirst beam portion 15 extends linearly in the X axis direction.According to such a shape, the first beam portion 15 has a relativelylarge torsional rigidity around the straight line A1. For example, thetorsional rigidity of the first beam portion 15 is larger than thetorsional rigidity of the second beam portion 14.

The mirror 16 is disposed on a surface of the first movable portion 13facing the cap structure 30. The mirror 16 has a light reflection filmformed of a metal thin film or the like.

As described above, the mirror 16 flaps around the straight line A 2 andflaps around the straight line A 1. This flapping motion will be furtherexplained. First, the mirror structure 10 constitutes a first vibrationsystem in which the first movable portion 13 and the mirror 16 serve asmass elements and the pair of first beam portions 15 serve as elasticelements. This first vibration system has a resonance frequency based ona total mass of the first movable portion 13 and the mirror 16 and anelastic coefficient of the first beam portion 15. Hereinafter, theresonance frequency of the first vibration system is referred to as afirst resonance frequency. More specifically, since the first vibrationsystem concerns flapping around the straight line A1 (reciprocatingrotational motion), the total mass is a moment of inertia around thestraight line A1, and the elastic coefficient is the torsional rigidityof the first beam portion 15.

Furthermore, the mirror structure 10 constitutes a second vibrationsystem in which the second movable portion 12, the first movable portion13 and the mirror 16 serve as mass elements and the pair of second beamportions 14 serve as elastic elements. This second vibration system hasa resonance frequency based on a total mass of the second movableportion 12, the first movable portion 13 and the mirror 16 and anelastic coefficient of the second beam portion 14. Hereinafter, theresonance frequency of the second vibration system is referred to as asecond resonance frequency. More specifically, since the secondvibration system concerns flapping around the straight line A2(reciprocating rotational motion), the total mass is a moment of inertiaaround the straight line A2, and the elastic coefficient is thetorsional rigidity of the second beam portion 14.

Here, the moment of inertia of the first vibration system is smallerthan the moment of inertia of the second vibration system by a moment ofinertia of the second movable portion 12. In addition, the torsionalrigidity of the first vibration system is larger than the torsionalrigidity of the second vibration system. The resonance frequency (moreaccurately, natural frequency) is inversely proportional to the momentof inertia (mass) and is proportional to the torsional rigidity (elasticcoefficient). Therefore, the resonance frequency of the first vibrationsystem is larger than the resonance frequency of the second vibrationsystem.

As shown in FIG. 4, the mirror structure 10 further includes a secondcoil 17 a and a first coil 18 a. The second coil 17 a is disposed in thesecond movable portion 12. The second coil 17 a cooperates with thelower magnetic body 20 (refer to FIG. 2) and the cap structure 30 (referto FIG. 2) to generate an electromagnetic force which flaps the mirror16 around the straight line A2 (refer to FIG. 3). Therefore, the secondcoil 17 a, the lower magnetic body 20, and the cap structure 30constitute a second drive portion D2. The second drive portion D2 isphysically connected to a first drive portion D1. The second coil 17 ahas a rectangular shape when seen in the Z direction. In the followingdescription, it is assumed that a rectangle includes a square. Thesecond coil 17 a is electrically connected to a pair of pads 17 c and 17c on the support portion 11 by a wiring 17 b disposed on one second beamportion 14. Therefore, a current is supplied to the second coil 17 a bysupplying the current between the pair of pads 17 c and 17 c. The firstcoil 18 a is disposed in the first movable portion 13. The first coil 18a cooperates with the lower magnetic body 20 and the cap structure 30 togenerate an electromagnetic force which flaps the mirror 16 around thestraight line A1. Accordingly, the first coil 18 a, the lower magneticbody 20 (refer to FIG. 2), and the cap structure 30 (refer to FIG. 2)constitute the first drive portion D1. Therefore, the first driveportion D1 is physically connected to the mirror 16. In addition, thefirst coil 18 a has a rectangular shape when seen in the Z direction.The first coil 18 a is electrically connected to the pair of pads 18 cand 18 c on the support portion 11 by a wiring 18 b disposed on thefirst beam portion 15, the second movable portion 12 and the othersecond beam portion 14. Therefore, a current is supplied to the firstcoil 18 a by supplying the current between the pair of pads 18 c and 18c.

The mirror structure 10 having the above-described configuration isintegrally formed by forming the second movable portion 12, the firstmovable portion 13, the second beam portion 14, and the first beamportion 15, for example, by performing a process, such as anisotropicetching, on a semiconductor substrate such as silicon.

As shown in FIG. 2, the lower magnetic body 20 has a rectangularparallelepiped shape integrally formed. The lower magnetic body 20 isdisposed on a back surface side of the surface of the mirror structure10 on which the mirror 16 is disposed, that is, on a negative side ofthe Z axis.

The lower magnetic body 20 has a first magnetic portion 21, a secondmagnetic portion 22, and a third magnetic portion 23. The first magneticportion 21 and the second magnetic portion 22 are disposed in adirection intersecting a direction in which the respective sides of thesecond coil 17 a and the first coil 18 a extend (that is, the X axisdirection and the Y axis direction). More specifically, the firstmagnetic portion 21 and the second magnetic portion 22 are disposed onone end side and the other end side of a bottom surface of the lowermagnetic body 20 in a diagonal direction. The third magnetic portion 23is disposed between the first magnetic portion 21 and the secondmagnetic portion 22. Since the first magnetic portion 21, the secondmagnetic portion 22 and the third magnetic portion 23 are disposed inthis way, the first magnetic portion 21, the second magnetic portion 22,and the third magnetic portion 23 generate a magnetic field, forexample, in a direction parallel to a diagonal direction of a bottomsurface of the casing 40.

The cap structure 30 is a plate-shaped member and has a rectangularshape when seen in the Z axis direction. The cap structure 30 isdisposed on a surface side of the mirror structure 10 on which themirror 16 is disposed, that is, on the positive side of the Z axis. Thecap structure 30 may be formed using, for example, a neodymium typemagnet or a samarium cobalt type magnet. A first region 31 and a secondregion 32 are disposed in a direction intersecting a direction in whicheach side of the second coil 17 a and the first coil 18 a extends (thatis, the X axis direction and the Y axis direction).

Incidentally, it has already been described that the resonance frequencyof the first vibration system is higher than the resonance frequency ofthe second vibration system. On the basis of this relationship, in thefollowing explanation, a configuration relating to the first vibrationsystem may be explained using the name of “fast.” For example, thestraight line A1 related to the first vibration system may be alsoreferred to as a “fast axis” (first drive axis), the resonance frequencyof the first vibration system may be also referred to as a “fast axisresonance frequency,” and the first coil relating to the first vibrationsystem may be also refer to as a “fast axis coil,” On the other hand, aconfiguration relating to the second vibration system may be describedusing the name of “slow.” For example, the straight line A2 relating tothe second vibration system may be also referred to as a “slow axis”(second drive axis), the resonance frequency of the second vibrationsystem may be also referred to as a “slow axis resonance frequency,” andthe second coil relating to the second vibration system may be alsoreferred to as a “slow axis coil.”

FIG. 5 is a block diagram showing a configuration of the control unit 3.The control unit 3 generates a driving signal for controlling the mirrorunit 2. The control unit 3 includes a controller 51, a fast axis coildrive circuit 52, a slow axis coil drive circuit 53, and a signalextracting portion 54.

The controller 51 generates a fast axis control signal (first controlsignal) N1 a (refer to FIG. 6A) and a slow axis control signal (secondcontrol signal) N2 a (refer to FIG. 6B). The fast axis control signal N1a is a control signal for flapping the mirror 16 around the fast axis A1f. The fast axis control signal N1 a is a signal including a componentof the fast axis resonance frequency which is the resonance frequency ofthe first vibration system. The controller 51 sets a waveform of thefast axis control signal N1 a to a sinusoidal waveform and sets afrequency (fast axis control frequency) of the fast axis control signalN1 a to the fast axis resonance frequency (first value). The waveform ofthe fast axis control signal N1 a is not limited to the sinusoidalwaveform and may be another shape such as a rectangular shape. A slowaxis control signal N2 a is a control signal for flapping the mirror 16around the straight line A2. The controller 51 sets a waveform of theslow axis control signal N2 a to a sawtooth waveform or a triangularwaveform and also sets a frequency (slow axis control frequency) of theslow axis control signal N2 a. The slow axis control frequency isgenerally set to be lower than the slow axis resonance frequency (secondvalue). In general, since the slow axis resonance frequency (secondvalue) is about 1/100 to 1/1000 of the fast axis resonance frequency(first value), the second value is smaller than the first value. Thewaveform of the slow axis control signal N2 a is not limited to thesawtooth waveform or the triangular waveform.

Here, the frequency of the fast axis control signal N1 a isappropriately changed according to the state of the mirror unit 2. Thefast axis resonance frequency changes according to an environment inwhich the mirror unit 2 is disposed and a use time. For example, when atemperature changes, a torsional rigidity of a material of the firstbeam portion 15 changes, and thus the fast axis resonance frequency alsochanges. Accordingly, when the frequency of the fast axis control signalN1 a is set to a preset fixed value, the frequency of the fast axiscontrol signal N1 a may deviate from an actual fast axis resonancefrequency (i.e., the first value). Therefore, the controller 51 has aconfiguration which appropriately adjusts the frequency of the fast axiscontrol signal N1 a. The configuration which adjusts the frequency ofthe fast axis control signal N1 a will be described later in detail.

The fast axis coil drive circuit 52 is connected to the controller 51and receives the fast axis control signal N1 a from the controller 51.The fast axis coil drive circuit 52 generates a fast axis driving signalN1 (refer to FIG. 6C) according to the fast axis control signal N1 a.Then, the fast axis coil drive circuit 52 is electrically connected tothe fast axis coil 18 f and outputs the fast axis driving signal N1 tothe fast axis coil 18 f. The slow axis coil drive circuit 53 isconnected to the controller 51 and receives the slow axis control signalN2 a from the controller 51. The slow axis coil drive circuit 53generates a slow axis driving signal N2 (refer to FIG. 6D) according tothe slow axis control signal N2 a. Then, the slow axis coil drivecircuit 53 is electrically connected to the slow axis coil 17 s andoutputs the slow axis driving signal N2 to the slow axis coil 17 s.

The signal extracting portion 54 is electrically connected to the slowaxis coil drive circuit 53 and the slow axis coil 17 s. That is, thesignal extracting portion 54 is electrically connected to a slow axisdrive portion (second drive portion D2). The signal extracting portion54 acquires a synthesized signal N3 (refer to FIG. 6E) output from theslow axis coil 17 s. Then, the signal extracting portion 54 extracts aninduced signal N4 (refer to FIG. 6F) used for generating the frequencyof the fast axis control signal N1 a from the acquired synthesizedsignal N3. The signal extracting portion 54 outputs the extractedinduced signal N4 to the controller 51.

Here, the inventors has found that the fast axis coil 18 f and the slowaxis coil 17 s are magnetically coupled to each other, and when the fastaxis coil 18 f flaps, a counter electromotive force is generated in theslow axis coil 17 s in accordance with the flapping. A signal resultingfrom this counter electromotive force is the induced signal N4. Thisinduced signal N4 is obtained by the signal extracting portion 54. Thesignal extracting portion 54 extracts the induced signal N4 from thesynthesized signal N3 obtained from the slow axis coil 17 s. Here, thesynthesized signal N3 (refer to FIG. 6E) input to the signal extractingportion 54 includes the slow axis driving signal N2 (refer to FIG. 6D)in addition to the induced signal N4 (refer to FIG. 6F) caused by thecounter electromotive force. Therefore, the signal extracting portion 54extracts the induced signal N4 from the synthesized signal N3 using asignal amplifier (signal amplifier portion) 54 a (signal amplificationportion), a signal filter (signal filter portion) 54 b, or the like. Forexample, the signal amplifier 54 a amplifies a frequency componentincluded in the induced signal N4. Further, the signal filter 54 bpasses the frequency component included in the induced signal N4 andattenuates a frequency component included in the slow axis drivingsignal N2. The signal extracting portion 54 may include both the signalamplifier 54 a and the signal filter 54 b, or may include one of them.

Here, a frequency band extracted by the signal extracting portion 54will be described. As shown in FIG. 7, a frequency of a band BAextracted by the signal extracting portion 54 is larger than at leastthe slow axis resonance frequency Frs.

For example, a first range (F1≤F≤F2) shown in a band B1 is suitable asthe band extracted by the signal extracting portion 54. A first lowerlimit frequency (F1) is smaller than the fast axis resonance frequency(Frf) and larger than the frequency (Fds) of the slow axis drivingsignal N2 and the slow axis resonance frequency (Frs). A first upperlimit frequency (F2) is larger than the fast axis resonance frequency(Frf). Further, a second range (F3≤F≤F2) shown in a band B2 is suitableas the band extracted by the signal extracting portion 54. A secondlower limit frequency (F3) is equal to or lower than the slow axisresonance frequency (Frs) and also larger than the frequency (Fds) ofthe slow axis driving signal N2. That is, the second lower limitfrequency (F3) does not include the frequency (Fds) of the slow axisdriving signal N2.

On the other hand, a third range (F4≤F≤F2) shown in a band B 3 is notsuitable as the band extracted by the signal extracting portion 54. Athird lower limit frequency (F4) is equal to or lower than the frequency(Fds) of the slow axis driving signal N2. Also, a fourth range (F5≤F≤F6)shown in a band B4 is not suitable as the band extracted by the signalextracting portion 54. A fourth lower limit frequency (F5) is largerthan the slow axis resonance frequency (Frs). A second upper limitfrequency (F6) is larger than the slow axis resonance frequency (Frs)and also smaller than the fast axis resonance frequency (Frf).

Hereinafter, the configuration and operation of the controller 51 willbe specifically described. FIG. 8 is a block diagram showing theconfiguration of the controller 51.

The induced signal N4 generated in the slow axis coil 17 s depends on afrequency and an amplitude of the flapping of the fast axis coil 18 f.Therefore, it is possible to know a flapping state of the mirror 16around the fast axis A1 f by observing the induced signal N4. In otherwords, the induced signal N4 is related to the fast axis resonancefrequency, not the fast axis driving signal N1. FIG. 9 shows timewaveforms G1, G2, and G3. The time waveform G1 shows the induced signalN4 when the frequency of the fast axis driving signal N1 coincides withthe fast axis resonance frequency (22.05 kHz). The time waveform G2shows the induced signal N4 when the frequency of the fast axis drivingsignal N1 coincides with a frequency (22.06 kHz) obtained by adding 10Hz to the fast axis resonance frequency. The time waveform G3 shows theinduced signal N4 when the frequency of the fast axis driving signal N1coincides with a frequency (22.04 kHz) obtained by subtracting 10 Hzfrom the fast axis resonance frequency. As can be seen from FIG. 9, forexample, when the fast axis resonance frequency coincides with thefrequency of the fast axis driving signal N1, a difference (phasedifference) between a phase of the fast axis driving signal N1 and aphase of the flapping of the mirror 16 around the fast axis A1 f is aconstant value (for example, zero). On the other hand, when the fastaxis resonance frequency does not coincide with the frequency of thefast axis driving signal N1, a difference (phase difference) occursbetween the phase of the fast axis driving signal N1 and the phase ofthe flapping of the mirror 16 around the fast axis A1 f. That is, it ispossible to know whether or not the flapping of the mirror 16 around thefast axis A1 f is in the resonance state by obtaining the phasedifference (refer to the phase differences Δφ 1 and Δφ 2 in FIG. 9)between the phase of the fast axis driving signal N1 and the phase ofthe induced signal N4 generated in the slow axis coil 17 s. Therefore,the frequency of the fast axis driving signal N1 may be adjusted so thatthe phase difference between the phase of the fast axis driving signalN1 and the phase of the induced signal N4 generated in the slow axiscoil 17 s becomes a constant value (for example, zero).

Therefore, the controller 51 adjusts the frequency of the fast axiscontrol signal N1 a so that the phase difference is close to theconstant value (for example, zero). As shown in FIG. 8, the controller51 includes a control portion 61, a slow axis waveform generatingportion 62, and a fast axis waveform generating portion 63. The controlportion 61 controls operations of the slow axis waveform generatingportion 62 and the fast axis waveform generating portion 63.

The slow axis waveform generating portion 62 generates a slow axiscontrol signal N2 a having a sawtooth waveform. Additionally, the slowaxis waveform generating portion 62 outputs a generated signal to theslow axis coil drive circuit 53.

The fast axis waveform generating portion 63 generates the fast axiscontrol signal N1 a having a sinusoidal waveform. Additionally, the fastaxis waveform generating portion 63 outputs the fast axis control signalN1 a to the fast axis coil drive circuit 52.

The fast axis waveform generating portion 63 includes a phase comparator63 a, a loop filter 63 b, and a voltage controlled oscillator 63 c. Dueto such a configuration, the fast axis waveform generating portion 63has a function as a so-called phase lock loop (PLL). That is, the fastaxis waveform generating portion 63 synchronizes the phase of the fastaxis control signal N1 a generated by the voltage controlled oscillator63 c with the phase of the induced signal N4 input from the signalextracting portion 54. The phase comparator 63 a obtains a phasedifference by comparing the induced signal N4 input from the signalextracting portion 54 with the fast axis control signal N1 a input fromthe voltage controlled oscillator 63 c. Then, the phase comparator 63 aoutputs a phase signal corresponding to the phase difference to the loopfilter 63 b. The loop filter 63 b obtains a processed phase signal byattenuating unnecessary high frequency components included in the phasesignal. Then, the loop filter 63 b outputs the processed phase signal tothe voltage controlled oscillator 63 c. The voltage controlledoscillator 63 c outputs a frequency corresponding to a magnitude(voltage) of the processed phase signal input from the loop filter 63 b.

Continuously, a drive method of the mirror device 1 will be described.FIG. 10 is a diagram showing main steps in the mirror drive method. Asshown in FIG. 10, first, a step (flapping step) S1 of flapping themirror 16 around the fast axis A1 f is performed. This step S1 isperformed by the controller 51 of the control unit 3, the fast axis coildrive circuit 52 and the fast axis coil 18 f. Next, a step (acquiringstep) S2 of acquiring the synthesized signal N3 from the slow axis driveportion D2 is performed. This step S2 is performed by the slow axis coil17 s and the signal extracting portion 54 of the control unit 3.

Next, a step (extracting step) S3 of extracting the induced signal N4from the synthesized signal N3 is performed. This step S3 is performedby the signal extracting portion 54 of the control unit 3. Next, a step(generating step) S4 of generating the fast axis control signal N1 a isperformed according to the induced signal N4. This step S4 is performedby the controller 51 of the control unit 3. More specifically, the stepS4 is performed by the control portion 61 of the controller 51, the fastaxis waveform generating portion 63, the voltage controlled oscillator63 c, the loop filter 63 b, and the phase comparator 63 a.

The phase difference between the phase of the fast axis control signalN1 a and the phase of the induced signal N4 is close to a constant value(for example, zero) by repeating the steps S1, S2, S3 and S4. Therefore,since the frequency of the fast axis control signal N1 a is maintainedat the fast axis resonance frequency (Frf), the flapping of the mirror16 around the fast axis A1 f is maintained in the resonance state.

In the mirror unit 2, the mirror 16 is flapped around the fast axis A1f. While the mirror 16 flaps around the fast axis A1 f, the signalextracting portion 54 obtains the synthesized signal N3 from the slowaxis drive portion D2. Specifically, the signal extracting portion 54obtains the synthesized signal N3 from the slow axis coil 17 s of theslow axis drive portion D2. The synthesized signal N3 includes theinduced signal N4. The induced signal N4 is a signal generated in theslow axis drive portion D2 due to an operation of flapping the mirror 16around the fast axis A1 f. That is, since the induced signal N4 iscaused by the operation of the mirror 16, the frequency of the inducedsignal N4 corresponds to the frequency in the flapping of the mirror 16with respect to the fast axis A1 f. The frequency of the flapping of themirror 16 with respect to the fast axis A1 f is higher than thefrequency of the mirror 16 with respect to the slow axis A2 s.Therefore, it is possible to easily extract the induced signal N4 fromthe synthesized signal N3 obtained from the slow axis drive portion D2.Additionally, a signal generating portion 50 is electrically connectedto the signal extracting portion 54 and the fast axis drive portion(first drive portion D1) and generates a driving signal to be suppliedto the fast axis coil 18 f according to the induced signal N4.Therefore, a result of flapping the mirror 16 by the fast axis coil 18 fcan be obtained as the induced signal N4 from the slow axis coil 17 s.Accordingly, since a feedback loop system relating to the flapping ofthe mirror 16 with respect to the fast axis A1 f is formed, it ispossible to reliably drive the mirror 16 with respect to the fast axisA1 f in the resonance state.

The above-described embodiment shows an example of the mirror device andthe drive method of the mirror. The mirror device and the drive methodof the mirror are not limited to the mirror device and the mirror drivemethod according to the embodiment and may be modified or applied toanother as long as the gist described in each claim is not changed.

In the above-described embodiment, the mirror 16 was flapped around thefast axis A1 f and the slow axis A2 s, but the present disclosure is notlimited to this configuration. For example, the mirror 16 may beconfigured to flap only around the fast axis A1 f. Even in this case,when the mirror 16 is flapped around the fast axis A1 f, a counterelectromotive force is generated in the slow axis coil 17 s. Therefore,the feedback loop system can be easily constituted by using this counterelectromotive force, and thus the mirror 16 can be reliably driven inthe resonance state.

In the above-described embodiment, the fast axis waveform generatingportion 63 has adjusted the frequency of the fast axis control signal N1a according to the phase difference between the phase of the fast axiscontrol signal N1 a and the phase of the induced signal N4. As can beseen from FIG. 9, the difference between the frequency of the fast axiscontrol signal N1 a and the fast axis resonance frequency affects notonly the phase difference but also the amplitude of the induced signalN4. Therefore, the frequency of the fast axis control signal N1 a may beadjusted according to the amplitude of the induced signal N4. When thefrequency of the fast axis control signal N1 a is shifted from the fastaxis resonance frequency, the flapping of the mirror 16 is not in theresonance state. Then, a flapping angle of the mirror 16 of which theflapping is not in the resonance state is smaller than a flapping angleof the mirror 16 of which the flapping is the resonance operation. Whenthe flapping angle is small, a magnitude of a fluctuation of themagnetic field generated by the fast axis coil 18 f also decreases.Therefore, a magnitude of the counter electromotive force (that is, theamplitude of the induced signal N4) generated in the slow axis coil 17 salso decreases (refer to amplitudes H1, H2 and H3 in FIG. 9). Therefore,the fast axis waveform generating portion 63 sweeps the frequency of thefast axis driving signal N1 in a predetermined frequency band. Then, thefast axis waveform generating portion 63 determines that the frequencyat which the amplitude of the induced signal N4 has a maximum value isthe fast axis resonance frequency. Since the feedback loop system can beeasily constituted even by adjusting the frequency of the fast axisdriving signal N1 using such amplitude, the mirror 16 can be reliablydriven in the resonance state.

In the above-described embodiment, the phase synchronization function inthe fast axis waveform generating portion 63 has been configured as ananalog circuit. The phase synchronization function in the fast axiswaveform generating portion 63 may be configured not only as an analogcircuit but also as a digital circuit (refer to FIG. 11) and may beconfigured as a combination of the analog circuit and the digitalcircuit (refer to FIG. 12).

As shown in FIG. 11, a controller 51A configured as a digital circuithas a digital control portion 61A, a slow axis waveform generatingportion 62A, and a fast axis waveform generating portion 63A. Thedigital control portion 61A controls operations of the slow axiswaveform generating portion 62A and the fast axis waveform generatingportion 63A. The slow axis waveform generating portion 62A generates aslow axis control signal N2 a provided to the slow axis coil drivecircuit 53. The slow axis waveform generating portion 62A includes a DAconverter 62 a. The DA converter 62 a converts the slow axis controlsignal N2 a output as a digital value from the digital control portion61A to the slow axis waveform generating portion 62A into an analogvalue. Then, the DA converter 62 a outputs the slow axis control signalN2 a converted into the analog value to the slow axis coil drive circuit53. The fast axis waveform generating portion 63A generates the fastaxis control signal N1 a provided to the fast axis coil drive circuit52. The fast axis waveform generating portion 63A includes an ADconverter 63 d and a DA converter 63 e. The AD converter 63 d receivesthe induced signal N4 which is an analog value from the signalextracting portion 54 and converts the induced signal N4 into a digitalvalue. Then, the AD converter 63 d outputs the induced signal N4converted into the digital value to the digital control portion 61A. Thedigital control portion 61A outputs the fast axis control signal N1 a,of which the frequency has been adjusted according to the induced signalN4, as a digital value to the DA converter 63 e. In the controller 51A,the phase comparison is performed by the digital control portion 61A.The DA converter 63 e converts the fast axis control signal N1 a outputas a digital value from the digital control portion 61A to the fast axiswaveform generating portion 63A into an analog value. Then, the DAconverter 63 e outputs the fast axis control signal N1 a converted intothe analog value to the fast axis coil drive circuit 52.

As shown in FIG. 12, a controller 51B configured as a digital circuithas a digital control portion 61A, a slow axis waveform generatingportion 62A, and a fast axis waveform generating portion 63B. Since thedigital control portion 61A and the slow axis waveform generatingportion 62A have the same configuration as the digital control portion61A and the slow axis waveform generating portion 62A of the controller51A shown in FIG. 11, the detailed description thereof will be omitted.The fast axis waveform generating portion 63B includes a phasecomparator 63 a, an AD converter 63 d, and a DA converter 63 e. Thephase comparator 63 a obtains a signal related to the phase differencebetween the phase of the fast axis control signal N1 a output from theDA converter 63 e and the phase of the induced signal N4 output from thesignal extracting portion 54. Then, the phase comparator 63 a outputs asignal related to the phase difference to the AD converter 63 d. The ADconverter 63 d receives the signal related to the phase differenceoutput from the phase comparator 63 a and converts the signal related tothe phase difference into a digital value. Then, the AD converter 63 doutputs the signal converted into the digital value to the digitalcontrol portion 61A. In the controller 51B, the phase comparison isperformed by the phase comparator 63 a.

In the above-described embodiment, the signal extracting portion 54treats the induced signal N4 as a voltage. The signal extracting portion54 may treat the induced signal N4 as a current. In other words, thecounter electromotive force generated in the slow axis coil 17 s may behandled as fluctuation of the current. In this case, the induced signalN4 may be directly extracted from the synthesized signal N3 showing thefluctuation of the current. Further, as shown in FIG. 13, a control unit3C of the mirror device 1C may have a current-voltage conversion circuit58 between the slow axis coil 17 s and the signal extracting portion 54.Then, in the current-voltage conversion circuit 58, the synthesizedsignal N3 output as the fluctuation of the current may be converted intoa voltage, and then the converted synthesized signal N3 may be input tothe signal extracting portion 54.

Further, the mirror device 1 is used for a light irradiation device andan image acquisition device. For example, FIG. 14 shows a lightirradiation device 7 such as a head-up display or a projector. The lightirradiation device 7 includes a light source 71 and a mirror device 1and irradiates light onto an object S such as a front glass or a screen.FIG. 15 shows an image acquisition device 8 such as a microscope device.

For example, the microscope device includes a reflection type microscopeor a transmission type microscope, a fluorescence microscope, a confocalmicroscope, a light sheet microscope, and an STED microscope. The imageacquisition device 8 includes the light irradiation device 7, anobjective lens 81 which irradiates the object S with the light outputfrom the light irradiation device 7, a photodetector 82 which detectslight (for example, fluorescence or transmitted light, reflected light,or the like) generated in the object S according to the irradiation oflight, and a computer 83 which generates an image of the object S on thebasis of a detection signal outputted from the photodetector 82. Anexample of the photodetector 82 is an image sensor, a photodiode, aphotomultiplier, or the like. In addition, the light generated in theobject S may be detected by the photodetector 82 via the mirror device 1or may be detected by the photodetector 82 without passing through themirror device 1.

REFERENCE SIGNS LIST

-   -   1 Mirror device    -   2 Mirror unit    -   3 Control unit    -   10 Mirror structure    -   11 Support portion    -   12 Second movable portion    -   13 First movable portion    -   14 Second beam portion    -   15 First beam portion    -   16 Mirror    -   17 a Second coil    -   17 s Slow axis coil    -   18 a First coil    -   18 f Fast axis coil    -   20 Lower magnetic body    -   30 Cap structure    -   40 Casing    -   50 Signal generating portion    -   51, 51A, 51B Controller    -   52 Fast axis coil drive circuit    -   53 Slow axis coil drive circuit    -   54 Signal extracting portion    -   54 a Signal amplifier    -   54 b Signal filter    -   63 a Phase comparator    -   63 b Loop filter    -   63 c Voltage controlled oscillator    -   58 Current-voltage conversion circuit    -   61 Control portion    -   61A Digital control portion    -   62, 62A Slow axis waveform generating portion    -   62 a, 63 e DA converter    -   63, 63A, 63B Fast axis waveform generating portion    -   63 d AD converter    -   A1 f Fast axis    -   A2 s Slow axis    -   D1 First drive portion    -   D2 Second drive portion    -   N1 Fast axis driving signal    -   N2 Slow axis driving signal    -   N3 Synthesized signal    -   N4 Induced signal

1-12. (canceled) 13: A mirror device comprising: a mirror supported tobe rotatable around a first drive axis and supported to be rotatablearound a second drive axis intersecting the first drive axis; a firstdriver configured to rotate the mirror around the first drive axis; asecond driver configured to rotate the mirror around the second driveaxis; a signal filter configured to pass an induced signal including afrequency higher than a second resonance frequency to rotate the mirroraround the second drive axis from a synthesized signal obtained from thesecond driver; a signal generator configured to generate a drivingsignal which controls the first driver based on the induced signal. 14:The mirror device according to claim 13, wherein the signal generator isconfigured to generate the driving signal according to a phasedifference between a phase of the driving signal and a phase of theinduced signal. 15: The mirror device according to claim 14, wherein thesignal generator is configured to generate the driving signal so thatthe phase difference becomes a constant value. 16: The mirror deviceaccording to claim 15, wherein the constant value is zero. 17: Themirror device according to claim 13, wherein the signal generator isconfigured to generate the driving signal according to an amplitude ofthe induced signal. 18: The mirror device according to claim 17, whereinthe signal generator is configured to generate the driving signal sothat the amplitude of the induced signal increases. 19: The mirrordevice according to claim 13, wherein the signal filter is configured toattenuate a signal including a frequency smaller than the secondresonance frequency. 20: A mirror device comprising: a mirror supportedto be rotatable around a first drive axis and supported to be rotatablearound a second drive axis intersecting the first drive axis; a firstdriver configured to rotate the mirror around the first drive axis; asecond driver configured to rotate the mirror around the second driveaxis; a signal amplifier configured to amplify an induced signalincluding a frequency higher than a second resonance frequency to rotatethe mirror around the second drive axis from a synthesized signalobtained from the second driver; a signal generator configured togenerate a driving signal which controls the first driver based on theinduced signal. 21: The mirror device according to claim 20, wherein thesignal generator is configured to generate the driving signal accordingto a phase difference between a phase of the driving signal and a phaseof the induced signal. 22: The mirror device according to claim 21,wherein the signal generator is configured to generate the drivingsignal so that the phase difference becomes a constant value. 23: Themirror device according to claim 22, wherein the constant value is zero.24: The mirror device according to claim 20, wherein the signalgenerator is configured to generate the driving signal according to anamplitude of the induced signal. 25: The mirror device according toclaim 24, wherein the signal generator is configured to generate thedriving signal so that the amplitude of the induced signal increases.26: A light irradiation device for irradiating light onto an object,comprising: a light source configured to output the light, and themirror device according to claim 13 configured to scan the light outputfrom the light source. 27: An image acquisition device for acquiring animage of an object, comprising: a light irradiation device according toclaim 26; and a photodetector configured to detect light generated inthe object according to radiation of the light by the light irradiationdevice. 28: A light irradiation device for irradiating light onto anobject, comprising: a light source configured to output the light, andthe mirror device according to claim 20 configured to scan the lightoutput from the light source. 29: An image acquisition device foracquiring an image of an object, comprising: a light irradiation deviceaccording to claim 28; and a photodetector configured to detect lightgenerated in the object according to radiation of the light by the lightirradiation device.